This invention pertains to electrodes and more in particular to an improved method of coating an electrode with a ruthenium compound.
Metallic electrodes of various metals, commonly known as valve or film-forming metals, such as tantalum, titanium and tungsten, have been employed as electrodes, that is, anodes or cathodes, in electrolytic processes, for example, producing chlorates, hypochlorites or chlorine and alkali metal hydroxide from aqueous sodium chloride containing brines. U.S. Pat. Nos. 3,632,498; 3,711,385 and 3,776,834 describe coating such valve metals with activating oxides to improve the electrode performance over previously available electrodes.
A portion of the electrode activating coating is generally lost during use of the electrode in an electrolytic cell. When the electrode is coated with mixed ruthenium and titanium oxides, the loss of ruthenium during the electrolysis of an aqueous alkali metal chloride solution in U.S. Pat. Nos. 3,632,478 and 3,711,385 is less than 0.1 and 0.5 gram per ton of chlorine produced, respectively. When the oxide coating contains a substantial portion of tin dioxide as in U.S. Pat. No. 3,776,834, the ruthenium wear-rate is alleged to average 0.01 gram per ton of chlorine produced.
In view of the relatively limited supply of ruthenium available, it would be desirable to provide an efficient electrode suitable for use in the electrolysis of an alkali metal chloride which consumes only minor amounts of ruthenium.